Nonwovens are now commonly used as interlining. Cohesion of the nonwovens is obtained either by the addition of binders or by localized thermofusion, applying either on only those fibers known as thermofusible fibers which have the lowest melting point, in the case of a mixture of fibers, or on all the fibers of the nonwoven, in the case of a one-constituent nonwoven.
The characteristics of the final interlining are partly conditional upon these different binding methods.
European Patent No. 0 363 254 describes a thermobonding interlining which consists in a binder-free nonwoven and, since the bonding is not induced by heat, said interlining contains no additional thermofusible fibers. The aim of this patent was to obtain a thermobonding interlining of this type where the thermofusible resin would not come through the material, even in the case of a low g/m2 weight rate. According to said European Patent, said aim was reached with a nonwoven constituted of a web of g/m2 weight comprised between 50 and 150, produced from microfilaments of mean diameter comprised between 3 and 5 .mu.m, the intermingling of which microfilaments is obtained by high pressure streams of fluid.
Therefore, according to the teaching of said patent, the aim could only be reached with a g/m2 weight of 50.
But now, interlining has evolved to such an extent that g/m2 weight smaller than 50 can be used, for example 17 to 25 g/m2 for blouses, 25 to 35 g/m2 for front interlinings in women's clothing.
The problem arising is therefore that of finding a thermobonding interlining having a g/m2 weight less than 50 g/m2 without the risk of the thermofusible resin coming through the material.